Conventional communication systems (FIG. 1) and trunked communication systems (FIG. 2) generally comprise a communication resource allocator, a limited number of communication resources that may be transmitted by a limited number of repeaters, a plurality of communication units, a plurality of consoles, and may include a computer aided dispatcher (CAD). The communication resource allocator generally comprises a plurality of operator mux interface modules (OMI), a plurality of base interface modules (BIM), a plurality of audio expansion interface modules (AEI), at least one audio signal bus, a MUX common module, at least one data interface bus (not shown), and may include a CAD interface module (CIMI). Each BIM and each OMI source, as signal sources, representations of audio signals to the audio signal bus. Depending on the signal source to TDM slot assignment, the audio signal bus receives the representation of audio signals into assigned TDM slots. Some of the representations of audio signals, which may be digital audio signals, may be summed together to produce a resulting digital audio signal and placed onto the sink audio bus (not shown). The sink audio bus comprises a plurality of TDM slots, one for each of the signal destinations (BIMs and AEIs), and routes the resulting digital audio signal to the proper signal destination.
Occasionally (for example, once every 30 seconds), the communication resource allocator verifies the continuity of a TDM slot of the audio signal bus by prompting one of the signal sources, either BIM or an OMI, to transmit a test tone into its assigned TDM slot. Once the test tone is placed in the TDM bus, each of the signal sources monitors the particular TDM slot to determine if the test tone is received. If the signal sources receive the test tone, which may be any predetermined signal, continuity of that particular TDM slot is verified. The test tone is placed on the audio signal bus it is processed as any other digital audio signal, thus in order for the test tone to be muted, each of the components of the communication resource allocator contain tone detect software such that when a test tone is being transmitted in any TDM slot, the components ignore the test tone, i.e. treat it a null signal. If the components did not contain test tone detection software, the tone would pass to the signal destinations causing the tone and/or pops to present which may be offensive to some users of the system. In practice, one of the OMIs may provide the prompting for the tone testing and would assure that each TDM slot was tested.
A plurality of communication systems, conventional and/or trunked, may be operably coupled to each other via a processing multiplexer and a plurality of source and sink interface buses to form a communication system network. To substantially function within the communication system network and to function independently, each of the communication systems further comprises a processing multiplexer interface module. The processing multiplexer interface module interfaces the communication system with the processing multiplexer by sending to and receiving from the processing multiplexer digital audio signals and data. One of the functions of the processing multiplexer interface module, or ambassador interface mux interface module (AIMI), is to take the digital audio signals from each of the TDM slots of the audio signal bus and place them into a corresponding TDM slot of the source interface bus. Once the digital audio signals are placed into the source interface bus, the processing multiplexer extracts the digital audio signals from the source interface bus, processes at least some of the digital audio signals on a per communication system per signal destination basis to produce resulting digital audio signals. The resulting digital audio signals are subsequently routed to the appropriate signal destinations via the sink interface buses. For a more detailed description of a communication system network refer to co-pending patent application having Ser. No. 07/509,915.
In a communication system network, each of the communication systems still perform a continuity test of the TDM slots of the audio signal bus. However, if the test is performed as described above, the test tone would not be recognized by the AIMI and thus the AIMI would send the test tone to the processing multiplexer. Once in the processing multiplexer, the test tone would be treated as any other digital audio signal which could end up being sent to a multitude of signal destinations.
Therefore, a need exists for a method and apparatus that allows the processing multiplexer interface module to prevent undesired digital audio signals, including test tones, from being transmitted to the processing multiplexer.